Method of drawing a polyester tow and apparatus therefor



June 1959. HARUKI TAKIZAWA ETAL 3,

METHOD OF DRAWING A POLYESTER TOW AND APPARATUS THEREFOR Filed Sept. 9, 1966 Sheet of 3 June 17, 1 969 HARUKI TA Kl ZAWA ETAL 3,

METHOD OF DRAWING A POLYESTER TOW AND APPARATUS THEREFOR Filed Sept. 9, 1966 Sheet 2 0f3 J 1969 I HARUKI TAKIZAWA ETAL 3,

I METHOD OFDRAWING A POLYESTER TOW AND APPARATUS THEREFOR Filed Sept. 9, 1966 Sheet 3 of :5

T E p m H A E LM 6 w ms 9 mm H W m xm m AR C D ME Di. 2 T T F QQW. 0 P zoazm; EEO 2052B 3% THE CASE OF MONOFIL B WHERE THE DRAW POINTS DO NOT COME IN THE FIRST BATH.

3,450,811 METHOD OF DRAWING A POLYESTER TOW AND APPARATUS THEREFOR Haruki Takizawa and Akitomo Kitamura, Matsuyama-shi,

Japan, assignors to Teijin Limited, Osaka, Japan, a corporation of Japan Continuation-impart of application Ser. No. 268,422, Mar. 27, 1963. This application Sept. 9, 1966, Ser. No. 578,241

Int. Cl. D01d 5/12; 132% 17/02 U.S. Cl. 264290 3 'Claims ABSTRACT OF THE DISCLOSURE This invention relates to a method of drawing a polyester tow and an apparatus therefor. More particularly, the invention relates to a method and apparatus for producing draw points in the individual monofils of a tow of polyester containing above 80 mol percent of terephthalic acid as its acid component.

This is a continuation-in-part of copending application Ser. No. 268,422, filed on Mar. 27, 1963, and now abandoned.

A primary object of this invention is to provide a method and apparatus for producing draw points for drawing a polyester tow from which can be obtained products whose quality is highly uniform.

Another object of this invention is to provide in drawing a polyester tow a method and apparatus in which the heating and drawing of the tow is accomplished in such a manner that yarn breakages are few and that the unoriented portions are much less than that of the tow drawn by the prior art methods and apparatus.

A further object of the invention is to provide a method and apparatus for drawing synthetic fibers, wherein the productivity is high.

It is known to draw polyester filaments after their spinning to effect the orientation of the molecules longitudinally of the filament axis, and hence to obtain a valuable fiber. In general, the as spun filament has an excessive elongation as well as a low tenacity and is not serviceable as obtained. Hence, it is well-known to draw the filament to several times its initial length for making its tenacity and elongation suitable.

As such a drawing method, various proposals have been made heretofore. In this case, particularly when treating a tow consisting of a plurality of undrawn filaments, from the standpoint of the maintenance of uniformity in the temperature of the individual monofils to be heated, the drawing is most preferably carried out while passing the tow through a hot liquid. In the conventional heatingbath drawing apparatus, a heating bath of a prescribed temperature is provided between the feed rolls which deliver the yarn at a given speed and the draw rolls having a surface speed several times that of the feed rolls, in which heating bath the yarn is heated and drawn to several times its initial length.

Generally, when the heating and drawing of thermoplastic synthetic fibers are carried out using a hot liquid,

nited States Patent if the temperature of this hot liquid is unsuitably low, a great degree of deformation amounting to several times the initial length of the fibers becomes difficult, since the drawing is carried out in a state of insuflicient heating, i.e., in a state in which the molecular movement is insufiicient for effecting the reorientation of the molecules. This becomes the cause of a great amount of yarn breakages, particularly when the drawing is carried out at high speeds. On the other hand, when the temperature of the hot liquid is excessively high, the movement of the molecules constituting the yarn becoming exceedingly active, the orientation of the molecules substantially along the filament axis, as intended by the drawing, is not brought about in a part of the yarns, but merely a movement of the molecules with respect to each other occurs, with the consequence that only the denier of the yarn is reduced. The presence of partly unoriented filaments in the drawn yarns is exceedingly detrimental to the uniformity of the product quality, particularly the uniformity of the dyeability, tenacity and elongation. A contrariwise utilization of a method such as this for the manufacture of fine yarns is described in British patent specification No. 695,567 and is referred to as super drawing.

A temperature range intermediate of these two extremes is generally employed as the heating temperature in drawing, though even in this temperature range which is regarded as being the optimum there are observed breakages in the yarn as the admixture of unoriented portions. This tendency is particularly marked when the drawing speed is increased. Hence, there exist many points for dissatisfaction when considered from the standpoint of increasing the productivity.

It is commonly regarded that the causes for the occurrence of yarn breakage and unoriented fibers in the method of drawing undrawn, thermoplastic synthetic fibers, particularly an associated yarn consisting of a plurality of undrawn fibers, arise from such as irregularities in the drawing temperature, defective association of the yarn bundle, etc. We found, however, that yarn breakages and unoriented fibers still occurred even after a thoroughgoing removal of these causes and employment of what was regarded as an optimum temperature. An undrawn tow consists of a plurality of undrawn fibers in which there exist within or between the individual monofils slight irregularities in the degree and amount of crystallization. We found that in a method wherein such a tow is drawn in a single step by means of only a single bath having a single temperature, there was a problem in such a method per se.

As hereinbefore noted, in the case of a tow composed of at least several ten thousands of undrawn monofils, there exist irregularities in quality between the individual monofils as well as between portions of the same monofil, in consequence of which the optimum drawing temperature differs between the monofils. This invention has devised a method of drawing the individual monofils at their optimum drawing temperature. When it is conceived that monofil A is best drawn at a temperature T while another monofil B is best drawn at a temperature T which is somewhat higher than temperature T a method must be conceived in which the draw point is made to occur at the temperature T, in the case of the monofil A, whereas it is made to occur at the temperature T in the case of the monofil B.

The gist of this invention therefore resides in a method of drawing the monofils making up a tow, which comprises, in drawing a tow of polyester fibers between feed rolls and draw rolls without interposing other rolls therebetween, the steps of applying between said rolls a bath of a liquid maintained at a temperature 40-80 C. to produce in said bath the draw points of a major number of the monofils making up the tow and thereafter applying at least one bath containing a liquid whose temperature is maintained from to 40 C. higher than the liquid of said first bath but not in excess of 100 C. to produce the draw points of the monofils which were not drawn in the first bath. And for carrying out this method, an apparatus for drawing the monofils making up a tow is used, which comprises a first bath which is disposed between the feed and draw rolls, which stretch the polyester tow, at a point nearer to the feed rolls and containing a liquid maintained at a temperature of 4080 C., and at least one other bath disposed between the first bath and the draw rolls and containing a liquid whose liquid temperature is 540 C. higher than that of the liquid of the first bath but not in excess of 100 C., whereby the draw points of a major part of the monofils making up the tow are produced in the first liquid bath during the passage of the tow therethrough, while the monofils whose draw points were not produced in the first bath are produced in the other bath.

Reference will be had to the accompanying drawings for describing the accomplishment of the foregoing method.

FIG. 1 is a view in longitudinal section of an apparatus according to this invention, wherein two liquid baths are disposed in continuous fashion between the feed and draw rolls. FIG. 2 is a sectional view of the invention apparatus wherein the two liquid baths are disposed between the rolls separate from each other. FIGS. 3 and 4 are sectional views of the invention apparatus wherein three or more liquid baths are provided. FIGS. 5 and 6 are graphs showing the relationship between the draw tension/denier and the draw ratio.

In the case of the aforesaid irregularities of the individual monofils, the difference in the load-elongation curve, i.e., the relationship between the draw ratio and the tension required therefor at the various temperatures, is manifested differently.

If, for sake of simplicity, the temperature of the liquid of the first bath is indicated as T that for the liquid of the second bath as T a temperature somewhat higher than T and the room temperature as T the relationship between the draw ratio and the tension per denier (tension g./de.) required for the draw in the case of a monofil having the properties A is as shown in FIG. 5. Similarly, the same relationship in the case of a monofil having the properties B is shown in FIG. 6. If it is assumed that a monofil A is drawn at a draw ratio Do and its draw point comes in the second liquid bath having a temperature T the tension of the monofil entering the draw rolls is then by X This tension X is greater than the tension P which is necessary for producing the draw point int he first liquid bath having a temperature T but is less than the tension P the tension required to produce the draw point at room temperature. Hence, even though the draw is originally in the second bath, it spontaneously shifts to the first bath and is stabilized therein. In the case of the monofil B, as shown in FIG. 6, when it is drawn by the same draw ratio D0, its draw tension is shown by Y As this tension Y is less than the tensions Q and Q by which draw points are produced at the liquid temperature T and room temperature T the draw point is produced in the second bath only.

In practicing this invention, it is possible to choose the liquid temperature T so that the draw points of a major number of the monofils will come in the first bath. If the drawing is carried out at the temperature T, those monofils which are susceptible to breakage or remain undrawn can be caused to produce their draw points in the next following bath containing a liquid of higher temperature, thus making it possible to carry out the drawing operation without undue strain.

The optimum temperature of the bath in this invention should be one which carries out the drawing most smoothly, the choice being made in accordance with the class of material of which the filaments to be drawn are composed, the degree of the slight orientation that has taken place during the spinning operation and the degree irregularities and crystallization of the filaments. This temperature should, in general, be established at above the second order transition temperature of the polyester fiber to be drawn, the temperature of the first bath being set in a range between 40 and C.

In case the temperature of the first bath is relatively high and, as a result, the difference in temperature between the first and second baths is great, there is a possibility that the undrawn filaments which were drawn in the second bath become crystallized, thus making it impossible for their drawing to be accomplished. Consequently, it is preferred that there exist a relatively small difference between the temperatures of the two baths. Since the second bath must not be of a temperature in which the rate of crystallization of the undrawn filaments is enhanced greatly, it is desirable that this temperature does not exceed C. in the case of polyester fibers. In any event, the temperature difference between the two baths must be at least 5 C.

On the other hand, when the first bath wherein the initial drawing is carried out has a relatively low temperature, that of the second bath may be considerably high, but in the case of a temperature difference in excess of 40 C., the stable operation of the drawing is rendered difficult and the significance of this invention is lost. In this case, there is a danger that a major part of the draw points which are to be produced in the first bath are shifted to the second bath. Hence, this must be absolutely avoided.

Further, the results desired in this invention cannot be manifested just by disposing a plurality of bath next to the first bath, if the former are of a lower temperature than the latter. The reason is that, as shown in FIGS. 5 and 6, the filaments are not drawn in the baths of lower temperature unless the tension is higher. In this case, however, if at least one of the plurality of baths following the first bath in which draw points are produced is of a higher temperature than said first bath, the filaments which were not drawn in the first bath will be drawn in the bath having the higher temperature under similar conditions as hereinbefore described. In this case the temperatures of the first and second draw baths must have the foregoing temperature relationship.

Next, the reason why a liquid is used for heating the monofils will be described. In general, in the case of the polyester fibers, drawing effects can be manifested at a higher temperature with less tension than when a lower temperature is used. Hence, as a medium for heating the fibers, conceivable are the mediums of gas, liquid and solid by which heat can be directly transmitted to the fibers. As a solid medium there is one consisting of a draw pin and a heated plate which follows, but in the case of this method of drawing wherein the yarn is caused to contact and rub this solid heated member, the drawing of a part of the filaments is forcibly carried out at temperatures deviating from their suitable drawing tempera ture because of the greatness of the frictional contact among the monofils making up the tow, which results in part of the filaments being drawn entrained with other filaments, at temperatures not suitable for their drawing. In consequence, unsatisfactory drawn fibers are produced. For a similar reason, the technique in which a separate system of rolls or yarn guides are disposed between the feed and draw rolls and the drawing is carried out by the heat of resistance generated by subjecting the yarn to resistance likewise impairs the uniformity of drawing.

On the other hand, in the case of the use of a gaseous medium for heating, its thermal capacity is less than that of a liquid medium, and hence it is impossible to provide a plurality of monofils rapidly with a uniform temperature using an equipment of small scale. In consequence, the transmission of heat to the fibers to be drawn becomes nonuniform with such an equipment to cause the appearance of irregularities in the drawn fibers.

It should thus be apparent from the foregoing reasons that liquid is most suitable for use as the heating medium in this invention. Although water is most convenient as the bath liquid, ethylene glycol, glycerine, vegetable oils and other organic solvents may also be used. It is also permissible to use a liquid containing preservatives, lubricants and fiber swelling agent.

It is not an indispensable requisite of this invention that, prior to drawing, preheating must be done as in the case of US. Patent 2,918,346. Hence, a greater part of the draw points may -be permitted to occur in the first bath on the feed roll side. This method completely differs also from that in which three or more groups of rolls are employed and the drawing is carried out in a multistage fashion. Neither is it that in which for the purpose of fixing the unstable draw points a preheating zone is established to fix the draw points. It also differs from a drawing method as disclosed in US. Patent 2,533,013 in which are provided a pin between the feed rolls and draw rolls for fixing the draw points and effecting the drawing and a heat plate for heat setting the drawn yarn in the neighborhood of the maximum temperature of its crystallization and at the same time to effect the second stage drawing. In the present invention, the second and subsequent baths are essentially not for elfecting the heat setting of the yarn nor are they for effecting the second stage drawing, but their purpose is to carry out the first stage drawing of the unoriented portion by employing the heating-bath drawing by which most uniform heating effects are obtained.

The operation of these apparatuses described with reference to the drawing is as follows: FIGS. 1 and 2 illustrate one of the simplest of the embodiments, the case where two baths are used. The thick tow 1 comprising a collection of numerous ends of undrawn yarn is conducted by feed rolls 2 and after passing therethrough passes through two baths 3 and 4, both more than cm. long and disposed between the feed rolls 2 and the draw rolls 16 of greater surface speed than the former, to be conducted to said draw rolls. Since the drawn tow contains hot liquid therein, this is squeezed out by means of squeeze rolls 17. The hot liquid of each of the tanks 9, 18 is heated by the respective thermostatic heaters 10 and 19 from whence it is delivered to the respective hot liquid baths by means of pumps 11 and 12 via pipes 13, 14 and 15. The hot liquid which has overflowed returns to the hot liquid tanks 9 and 18 via the return pipes 8 and 22 respectively. The reference numeral 5 shows the hot liquor spray nozzles. The hot liquid heater may be provided in each of the baths as shown by the reference numerals 20 and 21. When the drawing speed is great, a downwardly flowing means such as indicated by 5 may also be provided for uniformalizing the bath temperature.

The first bath 3 and the second bath 4 may be constructed as in FIG. 1, or they may be of separate construction as in the case of the first bath 3 and second bath 4 of FIG. 2. It is also possible to make wall 23 on the outlet side of the first bath and wall 24 on the inlet side of the second bath in common. The height of the dam 6 on the side from which the tow enters the hot liquid bath is preferably made slightly lower than that of the dam 7 of the outlet side so as to ensure that not much difference will occur in the amount of hot liquid overflowing at the two points even when the tow advances.

In the foregoing instance, it is also possible to eliminate the overflow and circulating means of hot liquid from the first and second baths and instead carry out the heating of the hot liquid in the baths by employment of a thermostat in each of the baths to regulate the electric current to the hot liquid heaters 20 and 21 to thus maintain a constant temperature in each of the baths.

FIG. 3 is a partial view of an embodiment comprising three baths, the illustration being only of the bath portions thereof; 25, 26 and 27 indicate the three baths. The hot liquid circulating part, the heating means, etc., of FIG. 2 can 'be applied correspondingly in this case. FIG. 4 is a partial view showing the bath portion only of an embodiment consisting of a still greater multiplicity of baths. The reference numerals 28, 29, 30 and 31 indicate the baths, it. being possible to dispose a still greater number of baths between the baths 30 and 31. While in FIGS. 3 and 4 the individual baths are shown as being separate, it is also possible to construct the baths connectedly as in FIG. 1. The embodiment in which the bath temperature is gradually raised between the feed rolls and the draw rolls by means of a multistage construction is generally desirable.

Example 1 In drawing an undrawn tow of one million deniers consisting of 15-denier monofils of polyethylene terephthalate having an intrinsic viscosity of 0.60 in orthochlorophenol at 25 C. and a second order transition temperature of 67 C., a two-stage hot water bath apparatus as shown in FIG. 1 was employed. When the drawing was carried out with only a first bath of C. bath temperature and drawing the tow to 3.9x its initial length at a drawing speed of 100 meters per minute, the number of unoriented fibers contained in the drawn tow was 7.6 ends per 100,000 ends of IO-mm. monofils. When, according to this invention, the first bath was made 80 C. and the second bath C., and thus with a 1 0 C., difference while other conditions were the same, the number of unoriented fibers was zero end per 100,000 ends of 10-mm. monofils. A greater part of the drawn points were observed to be in the first bath. The number of unoriented fibers was measured by a method of dyeing them to a deep shade. The measurement of unoriented fibers in the following examples were carried out by this method.

Example 2 In drawing a polyester fiber comprising principally polyethylene terephthalate containing 11.8 mol percent of diethylene glycol and having an intrinsic viscosity of 0.52, a second order transition temperature of 54 C. and a softening point of 239.5 C., a two-stage hot water bath as shown in FIG. 1 was employed. An undrawn tow of one million deniers consisting of IS-denier monofils was drawn at a drawing speed of 80 meters per minute to 3.9 X its initial length.

The temperature of the first and second baths was varied as set forth in Tables I and II, and besides the number of unoriented fibers, the number of yarn breakage per 100,- 000 ends of l-meter monofils was also investigated. A greater part of the draw points were in the first bath in each experiment.

All the yarn breakage measurements made in the examples to be given hereinafter were made on a basis of a monofil length of l-meter as in this example.

When the drawing is carried out with a deficiency in the temperatures of the first and second baths or with the temperature of the second bath lower than that of the first bath, the number of unoriented fibers and yarn breakages become exceedingly numerous.

TABLE I.EXPERIMENTS ACCORDING TO THE PRESENT INVENTION Difference in temperature First between Number of bath temperature Second bath ternfirst and unoriented perature second fibers breakages 0.) baths 0.) (ends) (ends) Number of yarn TABLE II.OONI ROLS Difference in temperature First Second between Number of Number bath tcinbath ternfirst and unoriented of yarn Expci 1- perature perature second fib ers b reakages nicnt 0.) C.) baths C.) (ends) (ends) A None 30.5 80 B 60 50 1O 40. 2 135 C 00 56 4 32. 5 82 D 60 60 0 30. 5 75 E 50 62 3 l5. 4 12 Example 3 When the undrawn tow used in Example 2 was stored for 13 days in a room of 30 C. and relative humidity of 85%, it became so fragile as to render its drawing very difficult. This to was drawn in the two-stage hot water bath apparatus shown in FIG. 1. When drawing was carried out at 55 C. employing the first bath only, the drawing was difiicult, the number of yarn breakage and unoriented fibers being exceedingly numerous. On the other hand, when drawing was carried out with a bath temperature of 70 C., super drawing occurred in part of the yarns so as to result in the production of products of inferior quality.

When the drawing was carried out in accordance with the method of this invention employing a bath temperature of 55 C. for the first bath, 70 C. for the second bath and a temperature difference of 15 C. between the two, the number of unoriented fibers per 100,000 ends was 15.2 ends and the number of yarn breakage was 20 ends, thus making production possible. The drawing speed was 60 meters per minute.

Example 4 Using the undrawn tow used in Example 2, drawing to 3.9x was carried out while employing the apparatus as shown in FIG. 1 with a first bath water temperature of 63 C., a second bath water temperature of 73 C., and hence a temperature difference of C. beween the two, and at a drawing speed of 100 meters per minute, with a consequence that the number of unoriented fibers per 100,- 000 ends was 2.3 ends. Further, even when the drawing was effected at a drawing speed of 150 meters per minute using the same undrawn tow and the same draw ratio with a first bath water temperature of 65 C., second bath water temperature of 75 C., and hence a 10 C. difference between the two, the number of undrawn fibers mixed in the drawn fibers was only 3.5 ends per 100,000 ends. However, when a second bath was not employed, even though a drawing speed of 60 meters per minute was used, the number of undrawn fibers at the same draw ratio did not become greater than ends. A greater part of the draw points were all in the first bath. Therefore, it becomes possible to raise the drawing speed according to this method.

8 Example 5 When an undrawn tow of 430,000 deniers consisting of 2l-denier polyethylene tcrephthalate monofils having an intrinsic viscosity of 0.50 and a second order transition temperature of 69 C. was allowed to stand for 10 days in its wet state in a C. room it became very fragile.

In drawing this tow while employing an apparatus as shown in FIG. 1, when the temperature was varied variously between 50 and 95 C. in employing only the first bath, the number of unoriented fibers per 100,000 ends never became less than 35 ends. In addition, the number of yarn breakages was also large. On the other hand, when, in accordance with the present invention, a first bath of C. and a second bath of C. were used, making a 35 C. difference in temperature, exceedingly good results were obtained. Namely, the number of unoriented fibers per 100,000 ends did not exceed 7 ends while the yarn breakages were 5 ends per 100,000 ends.

We claim:

1. A method of drawing monofils making up a tow of polyester fibers between feed and draw rolls without interposing other rolls therebetween, said method comprising the steps of applying a first bath liquid maintained at a temperature ranging between 40 and 80 C., to said tow between said rolls to produce in said first bath the draw points of major number of the monofils, and thereafter applying to said tow at least one bath liquid whose temperature is maintained at from 5 to 40 C. higher than that of said first bath liquid but not exceeding C. to produce the draw points in said monofils which were not drawn in the first bath.

2. The method according to claim 1 wherein the polyester fiber used contains above 80 mol percent of terephthalic acid as acid component.

3. An apparatus for drawing polyester monofils making up a tow, said apparatus comprising a first bath containing a liquid maintained at a temperature ranging between 40 and 80 C. and disposed between the feed and draw rolls by which the tow is stretched, in a location closer to said feed rolls, and at least one other bath containing a liquid maintained from 5 to 40 C. higher than the temperature of the liquid of the first bath but not exceeding 100 C., whereby a major number of the draw points of the monofils making up the tow are produced in the first bath as the tow passes therethrough and the draw points of the monofils which were not produced in the first bath are produced in the other bath.

References Cited UNITED STATES PATENTS 2,465,319 3/ 1949 Whinfield et a1. 2,918,346 12/1959 Paulsen.

DONALD J. ARNOLD, Primary Examiner.

I. H. WOO, Assistant Examiner.

US. Cl. X.R. 181; 264-210 

